Firefox extension Stealther lets you browse the web without leaving a trace of your browsing session on your computer by disabling:

- Browsing History (also in Address bar)

- Cookies

- Downloaded Files History

- Disk Cache

- Saved Form Information

- Sending of ReferrerHeader

Okay, so there's plenty of instances when you might want to browse without a trace, and I'm certainly not suggesting that there's only one use for this extension, but it does bring to mind Safari's Private Browsing, aka Porn Mode. I'm not saying a thing, though - you kids go ahead and use it for whatever you use it for - ol' Lifehacker will just look the other way like so many willfully-ignorant parents.